Furnaces are used extensively in the smelting and converting of ferrous and non-ferrous ores and concentrates. Furnaces of this type are generally circular or rectangular, having a bottom wall (hearth), vertical walls comprised of refractory bricks and a roof or off-gas hood. Furnaces of this type are also characterized by a binding and support structure, the purpose of which is to maintain the refractory bricks of the hearth and walls in compression.
Adequate compression of the furnace walls, and particularly the hearth, is critical to maximize furnace campaign life and to prevent costly and potentially catastrophic furnace failure. During heating of the furnace to operating temperature, the individual bricks comprising the hearth and the walls expand, resulting in outward expansion of the hearth. Conversely, cooling of the furnace results in contraction of the individual bricks and overall shrinking of the furnace. If the compressive forces on the hearth or the walls are insufficient, gaps will be formed between the bricks during the cooling phase of the furnace operation. These gaps can be infiltrated with molten metal or other material, resulting in permanent growth of the furnace. Repetition of heating and cooling cycles results in further incremental expansion of the furnace (known as “ratcheting”), which usually results in a reduction of the furnace campaign life, by the potential for molten material infiltrating into the hearth refractory or excessive expansive forces exerted on the binding system.
Furnace binding systems are known for applying horizontally directed compressive forces on the walls and hearth of a furnace in order to control outward expansion of the furnace. Such binding systems are discussed in detail in the applicant's co-pending U.S. patent application Ser. No. 10/269,392, filed on Oct. 11, 2002.
The inventors have found that infiltration of materials into the joints between refractory bricks in a furnace wall can result in vertical expansion or “ratcheting” in the wall, which is also detrimental to furnace campaign life. At present, there are no furnace binding systems known to the inventors which are able to effectively control vertical expansion of the furnace walls.